Friday

October 9, 2015
Posted by **Andy** on Sunday, December 8, 2013 at 12:30pm.

(a) What is the angular speed of the ruler ω when it is at an angle θ=30∘? (in radians/sec)

ω=

unanswered

(b) What is the force exerted by the wall on the ruler when it is at an angle θ=30∘? Express your answer as the x component Fx and the y component Fy (in Newton)

Fx=

unanswered

Fy=

unanswered

(c) At what angle θ0 will the falling ruler lose contact with the wall? (0≤θ0≤90∘; in degrees) [hint: the ruler loses contact with the wall when the force exerted by the wall on the ruler vanishes.]

θ0=

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**Anonymous**, Sunday, December 8, 2013 at 1:25pmyes please.. that's the only question where I'm stuck too..

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**Teresa**, Sunday, December 8, 2013 at 1:26pmMe too!!!

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**ROMA**, Sunday, December 8, 2013 at 2:15pmHi Teresa, can you do rocket problem me pls?

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**Teresa**, Sunday, December 8, 2013 at 2:23pmp: percentage (4.5% is burned in 155s)

m:mass of rocket

u:fuelspeed in meter/s!

v=u*ln(1/(1-p))=1500*ln(1/0.955)

a=v/t = 69.065/155= 0.4455

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**ROMA**, Sunday, December 8, 2013 at 3:18pmHi Teresa, in my problem, question says The rocket burns 10 % of its mass in 290 s (assume the burn rate is constant).

What is the speed of the rocket after a burn time of 145.0 s?

How did you find 4.5% is burned in 155 sec? Pls.

Thank you very much

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**Teresa**, Sunday, December 8, 2013 at 3:58pmbecause they ask you for half of the time,

so in your case in 145 it gets burned 5% in 145 seconds

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**ROMA**, Sunday, December 8, 2013 at 8:17pmThank you very much Teresa. I got green check. Now time for rular one..

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**anon**, Sunday, December 8, 2013 at 8:42pmin the equation above what is the "ln"?

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**ROMA**, Sunday, December 8, 2013 at 8:52pm"ln" is like log..it is in your calculator

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**anon**, Sunday, December 8, 2013 at 9:00pmis the "u" the ejected fuel in m/s instead of km/s?

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**kumar**, Monday, December 9, 2013 at 3:15amhai Teresa can u help me for this Rocket question i don't know how to get 0.955 in the above ans !

Consider a rocket in space that ejects burned fuel at a speed of vex= 2.0 km/s with respect to the rocket. The rocket burns 11 % of its mass in 250 s (assume the burn rate is constant).

(a) What is the speed v of the rocket after a burn time of 125.0 s? (suppose that the rocket starts at rest; and enter your answer in m/s)

v=

unanswered

(b) What is the instantaneous acceleration a of the rocket at time 125.0 s after the start of the engines?(in m/s2)

a=